1. Field of the Invention
The present invention relates to a transmission control apparatus for an automotive vehicle, and more specifically to a transmission control apparatus for actuating a transmission on the basis of shift lever position signals generated by a shift lever position detector.
2. Description of the Prior Art
Conventionally, manual and automatic transmissions (speed change gears) are well known. In the manual transmission, since any appropriate gear change ratios can be selected by the driver, it is possible to obtain comfortable drive feeling. However, the clutch engage and disengage operations are troublesome for the driver. On the other hand, in the automatic transmission, since no clutch operations are required for the driver, it is possible to reduce the driver's fatigue. However, since the gear change ratios are changed in accordance with a predetermined pattern in general, there exists a problem in that it is difficult to obtain an optimum gear change ratio at all times according to every vehicle travelling condition, so that fuel consumption ratio inevitably increases.
To overcome the above-mentioned problem, recently transmissions provided with both the manual and automatic gear change functions have been widely used, by which gear change ratios can be selected manually without operating the clutch when the shift lever is set to one of fixed ranges and, and also selected automatically when set to a D (Driver) range. In the above-mentioned transmission, a transmission control apparatus for actuating a transmission on the basis of shift lever position signals generated by a shift lever position detector is often used in cooperation with a controller (microcomputer) mounted on an automotive vehicle. An example of the transmission control apparatus as described above is disclosed in Japanese Published Unexamined (Kokai) Patent Appli. No. 61-236958, as shown in FIG. 1.
In more detail, the transmission control apparatus comprises a transmission shift lever 101, a shift lever position detector 103, a controller (e.g. microcomputer) 105 and a transmission actuator (e.g. hydraulic valve) 107 to actuate a transmission 109. In FIG. 1, when the shift lever 101 is set to any one of shift lever positions, the shift lever position is detected by the shift lever position detector 103; an electric signal Sp indicative of a shift lever position is applied to the controller 105; the controller 105 discriminates the applied position signal and outputs an actuator control signal Sc representative of a selected shift lever position to the transmission actuator 107; and the transmission actuator 107 outputs a signal Sa to the transmission 109 to actuate the transmission 109 at a gear change ratio selected by the shift lever. Further, the transmission actuator 107 generates an end signal Se indicative of gear shift operation completion to the controller 105, so that the controller 105 stops outputting the actuator control signal Sc to the transmission actuator 107.
In the prior-art transmission control apparatus as described above, there exists a problem in that the transmission actuator 107 is erroneously activated, in spite of the fact that the shift lever is not operated or shifted, when external noise is superposed upon the actuator control signal Sc applied from the controller 105 to the transmission actuator 107.